He marked the passing of 100 days since his return to Downing Street with a vow that all schools will be given the chance to convert to academy status.

Asked about his future, the Prime Minister told BBC Radio 4's Today programme: "I stand absolutely by what I said. Ten years is a good long time to be Prime Minister and I stand by what I said.

"But I've got plenty to get on with, it's a full manifesto, a strong mandate for it and ... 100 days in I think people can see we are delivering the things we said we would - a tax-free minimum wage, more apprenticeships, capping welfare, making work pay. I think it's been a strong start."

The Prime Minister set out his plans for academies in an article in the Daily Telegraph, promising the the Government would recruit more academy sponsors and back head teachers to allow thousands more schools to break free of council control.

The Conservative leader placed the pledge at the heart of his One Nation vision and said his party would press on with public sector reform as Labour squabbled over its future.

Mr Cameron said he "profoundly believed" academy schools were the right way forward as he placed the schools at the heart of his public sector reforms - and accused Labour of "giving up" on making changes.

He said: "That is why in the first 100 days we have brought forward legislation to transform all failing schools into academies, and for the first time taken the power to convert coasting schools into academies too.

"But we have also seen how these freedoms can help all schools, with more than 3,000 good and outstanding schools already making the decision to become academies themselves.

"So, when Labour leadership contenders say they want to phase out academies, I say the opposite.

"I want every school in the country to have the opportunity to become an academy and to benefit from the freedoms this brings."

Currently, while planned legislation will convert failing or coasting schools, successful schools have to apply to change status. Thousands have done so since Mr Cameron became Prime Minister in 2010.

The Prime Minister defended the welfare cuts introduced by George Osborne in the Budget, insisting that the Tories would "make work pay".

Respected independent think-tank the Institute for Fiscal Studies found that the average low-paid worker on tax credits would "unequivocally" lose more from benefit cuts announced by the Chancellor than they would gain from the introduction of the national living wage, which will be worth £7.20 an hour to workers aged 25 or more - rising to £9 by 2020 - compared with £6.50 on the current national minimum wage.

IFS analysis suggested that the poorest tenth of society will lose around £800 a year as a result of tax and benefit changes in the years up to 2019 - equivalent to almost 7% of their net income - while the hardest-hit group will be the second-poorest tenth, losing around £1,300 a year.

But Mr Cameron defended the policy, telling Today the welfare reductions were needed for two reasons - cutting the deficit and increasing incentives to work.

"We still have a large budget deficit which we need to eliminate to secure the future for our economy and make sure our country is properly sustainable," he said.

"The second thing is we want to make sure that work always pays. Without the restrictions of the Liberal Democrats we were able to do something very radical but also very progressive."

Mr Cameron added: "If you look at a typical family where one person is on the minimum wage, with our changes to the national living wage, to the fact that we are increasing the amount you can earn before you pay tax, they will actually be better off.

"What our changes mean is that work will always pay. You will always be better off working, and working that extra hour.

"But if you are asking me, have we had to take difficult decisions in order to pay down the deficit and make sure that work always pays? Yes we have. But we have done it in a way that helps some of the lowest-paid people in our country because we are able to introduce the national living wage in such a powerful and progressive way."

Shadow chancellor Chris Leslie challenged Mr Cameron's defence of the welfare cuts by highlighting House of Commons Library analysis which showed some people on tax credits will keep only 7p of every extra pound they earn following the measures announced in the Budget.

He said: "By introducing a clawback of up to 93p for every extra £1 earned, David Cameron's claim to want to 'make work pay' is patently false. The Prime Minister shouldn't pretend that the minimum wage change can offset the far greater cuts in working tax credit which will penalise those who want to work and earn more.

"George Osborne's July Budget will hit those who want to get better jobs and salaries - not help them."

He added: "Labour will oppose this work penalty proposed in the tax credit changes."

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